things/img/scrall/screenshot.c

#include "screenshot.h"
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <xcb/composite.h>

Image get_screenshot(xcb_connection_t *conn, xcb_window_t wid) {
  xcb_generic_error_t *err = NULL;

  xcb_composite_redirect_window(conn, wid, XCB_COMPOSITE_REDIRECT_AUTOMATIC);

  xcb_get_geometry_cookie_t gg_cookie = xcb_get_geometry(conn, wid);
  xcb_get_geometry_reply_t *gg_reply = xcb_get_geometry_reply(conn, gg_cookie, &err);


  if (!gg_reply) {
    fprintf(stderr, "xcb: error: geometry: %d (wid: 0x%08x)\n", err->error_code, wid);
    return (Image){
      .data = 0, .width = 0, .height = 0, .format = 0, .mipmaps = 0
    };
  }

  int win_w = gg_reply->width;
  int win_h = gg_reply->height;
  int win_d = gg_reply->depth;
  assert(win_d == 32 || win_d == 24);

  free(gg_reply);

  xcb_pixmap_t win_pixmap = xcb_generate_id(conn);
  xcb_composite_name_window_pixmap(conn, wid, win_pixmap);

  xcb_get_image_cookie_t gi_cookie = xcb_get_image(conn, XCB_IMAGE_FORMAT_Z_PIXMAP, win_pixmap, 0, 0, win_w, win_h, (uint32_t)(~0UL));
  xcb_get_image_reply_t *gi_reply = xcb_get_image_reply(conn, gi_cookie, &err);

  if (!gi_reply) {
    fprintf(stderr, "xcb: error: get_image_reply: %d (wid: 0x%08x)\n", err->error_code, wid);
    return (Image){
      .data = 0, .width = 0, .height = 0, .format = 0, .mipmaps = 0
    };
  }

  int data_len = xcb_get_image_data_length(gi_reply);

  uint8_t *data = xcb_get_image_data(gi_reply);

  Image img = GenImageColor(win_w, win_h, BLANK);

  for (int i = 0; i < data_len; i += 4) {
    ((uint8_t *)img.data)[i + 0] = data[i + 2];
    ((uint8_t *)img.data)[i + 1] = data[i + 1];
    ((uint8_t *)img.data)[i + 2] = data[i + 0];
    ((uint8_t *)img.data)[i + 3] = win_d == 24 ? 0xff : data[i + 3];
  }
  free(gi_reply);

  return img;
}